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shingles (herpes zoster)

following an attack of chickenpox the herpes virus may become latent in dorsal root ganglion cells (or trigeminal ganglion cells), reactivation of the virus produces painful skin irritations in the dermatomal area innervated by the related ganglion

phantom limb sensations

following the amputation of a limb the patient often feels sensations which seem to orginate from the missing limb, usually sensation of pain (neuropathic pain--deafferentation pain)

likely explanation is reorganization of cortical maps, may be rearrangement or cortical input to area that formerly represented amputated limb

ex for amputated hand, touch pathways originating in face are likely to form new circuits within the primary somatosensory cortex (S1) that connect them with cortical neurons that would have otherwise become "jobless" (lacking innervation from the missing limb)-->phantom limb sensation evoked by touching face

headache

aspirin

effect of aspirin and other non-steroidal anti-inflammatory analgesics in controlling pain is due to its ability to inhibit the enzyme cyclo-oxygenase responsible for the synthesis of prostaglandins--agents which sensitize sensory afferent fibers

myopia

the focus of parallel lights (far vision) is anterior to the photosensitive elements of the retinal photoreceptors, objects positioned closer to the eye (near visioin) can still be focused on the retina even without the contribution of the usual mechanisms for near accommodation

vision is best during near vision, nearsightedness, treat with corrective lenses or corneal surgery

hyperopia

the focus of the parallel light rays (far vision) is beyond the retina, objects in the far distance from the eye can still be brought into focus by activating the mechanisms for near accommodation which increase the refractive power of the eye

near accommodation fails for objects close to the eye and reduces the ability for near vision

vision is best during far vision, farsightedness, treat with corrective lenses or corneal surgery

emmetropia

describes the state of vision where an object at infinity is in sharp focus with the eye lens in a neutral or relaxed state, this condition of the normal eye is achieved when the refractive power of the cornea and the axial length of the eye balance out, which focuses rays exactly on the retina resulting in perfect vision

papilledema

optic disk edema, important clinical sign which can indicate increased intracranial pressure, increased pressure compromises the venous drainage of the eye leading to dilation of the retinal veins, as a consequence the optic disc is pushed forward and the disk appears white rather than pink as in normal conditions